1. Field of the Invention
The present invention relates to ZnO films, methods for manufacturing the ZnO films, and luminescent elements. In particular, the present invention relates to a p-type ZnO film, a method for manufacturing the ZnO film, and a luminescent element including the ZnO film.
2. Description of the Related Art
Deposition of a ZnO film on a substrate has been studied for blue light-emitting diodes, solar cells, and the like. ZnO generally exhibits n-type conductivity as a result of adding a dopant such as Al. In order to form the pn junction, a p-type ZnO film is also necessary. However, it is difficult to form a p-type ZnO film.
A method for forming a p-type ZnO film is disclosed in a literature entitled xe2x80x9cp-Type Electrical Conduction in ZnO Thin Films by Ga and N Co dopingxe2x80x9d (Japan J. Appl. Phys., Vol. 38 (1999) pp. L1205-1207). In this method, a ZnO film is deposited on a glass substrate using a ZnO target doped with Ga while the inside of the vacuum chamber employed is maintained under an atmosphere of nitrogen gas, and the film is exposed to an excimer laser beam to form a p-type ZnO film by laser ablation.
However, a laser beam having a small spot size is used in the laser ablation process. Therefore, when a film is deposited on a substrate having a large diameter, the scanning length and the scanning time of the laser beam become very large. Accordingly, it takes a long time to cover the substrate with the film and the cost increases. Therefore it is difficult to put this method into practical use.
Accordingly, one object of the present invention is to provide a ZnO film having p-type conductivity and which can be easily formed on a large substrate, to provide a method for manufacturing the ZnO film, and to provide a luminescent element having the p-type ZnO film.
In order to overcome the problems described above, the present invention provides a ZnO film comprising ZnO as main material doped with a Group III element and a Group V element according to one preferred embodiment of the present invention. By doping with a Group III element and a Group V element to the film which mainly containing ZnO, a p-type ZnO film can be formed without performing laser ablation. Specifically, the p-type ZnO film of the present invention can be formed on a substrate by sputtering, ECR sputtering, CVD, MOCVD or MBE, and therefore, it can be formed at a speed higher speed than that of laser ablation and at low cost. Thus, the industrial productivity of p-type ZnO films can be increased.
The Group III element may be selected from the group consisting of Sc, Y, La, Ac, B, Al, Ga, In, Tl, lanthanides and actinides, and the Group V element may be selected from the group consisting of N, V, Nb, Ta, P, As, Sb and Bi. Preferably, the content of the Group III element is in the range of about 0.5% to 8% by weight and the content of the Group V element is in the range of about 1% to 16% by weight. Preferably, the content of the Group V element is higher than the content of the Group III element.
According to a methodological aspect, the present invention provides a method for manufacturing a ZnO film. The method includes the steps of: doping a material mainly containing Zn or ZnO with a Group III element and a Group V element to form a target; and depositing a ZnO film on a substrate using the target. The present invention is also directed to another method for manufacturing a ZnO film which method includes the steps of: doping a material mainly containing Zn or ZnO with a Group III element to form a target; depositing a ZnO film on a substrate using the target; and implanting Group V ions into the ZnO film. The Group III element and the Group V element may be contained in compounds, and specifically in oxides.
According to another preferred embodiment of the present invention, the present invention provides a ZnO film doped with a Group I element and a Group VII element and the film mainly contains ZnO. Preferably, the content of the Group I element is in the range of about 0.5% to 8% by weight and the content of the Group VII element is in the range of about 1% to 16% by weight. More, preferably, the content of the Group I element is about 0.5% to 7.5% and the content of the Group VII element is about 1 to 15%. Preferably, the content of the Group I element is higher than the content of the Group VII element. By doping a film mainly containing ZnO with a Group I element and a Group VII element such that the content of the Group I element is higher than that of the Group VII element, a p-type ZnO film can be formed without performing laser ablation. Specifically, the p-type ZnO film of the present invention can be formed on a substrate by sputtering, ECR sputtering, CVD, MOCVD or MBE, and therefore, it can be formed at a speed higher speed than that of laser ablation and at low cost. Thus, the industrial productivity of p-type ZnO films can be increased.
The ZnO film can be applied to luminescent elements, such as blue light-emitting diodes. By using the p-type ZnO film of the present invention to increase the manufacturing speed of the luminescent elements, mass productivity can be increased.